Based on the implications of this statement, it has been suggested by some players that the result of every melee or ranged attack is decided based on a single server-generated random number (a single "die roll" made internally on the server), checked against a server-side internal table for the attack.

This is the table that governs a melee attack by a mob and a melee auto attack by a player.

The tables are laid out in descending order of the precedence of one attack result over another. That is to say, the entries at the top of the table take precedence over the entries below them. This precedence order is from Blizzard, and as such is accurate. What this table means is this:

Every melee attack (except for yellow-damage special attacks dealt by players, as described in the next section) has a chance to miss, to be dodged, to be parried, to be blocked, to be a glancing blow, to be a critical, and to be a crushing blow. Anything left over is an ordinary hit.

The chances listed in your general spellbook tab (for you to Dodge, Parry, or Block) are absolute percentages. If you have a listed dodge chance of 4.5%, then on average 4.5% of all melee attacks made against you by a mob of equal level will be dodged, not merely 4.5% of those melee attacks that didn't miss you.

Some melee attacks have a 0% chance for some of these attack results; e.g., an auto-attack made by a player has a 0% chance of being a crushing blow, an attack made by a mob has a 0% chance of being a glancing blow, an attack made against a player without a shield has a 0% chance of being blocked, etc..

For mob and white-damage melee attacks, there is no such thing as a blocked crushing blow, a parried crit, a missed glancing blow, etc.. All of these possible attack results are mutually exclusive.

If the total chances of all the entries above the bottom of the table reach or exceed 100%, the attack cannot be an ordinary hit.

If the total combined chance of a miss, dodge, parry, or block is 100% or higher, not only can the attack not be an ordinary hit, the attack also cannot be a crit or a crushing blow.

*Only players and pets versus mobs†Only mobs versus players and pets, and only when the attacker is at least 4 levels higher than the target. (Note: Mobs seem to be able to crush each other as of Patch 3.20)

Suppose a mob of equal level is attacking your warrior character in melee. Your Defense skill is maxed out for your level, but has no other bonuses. In the general tab of your spell book, you see that your listed Dodge chance is 4.5%, your listed Parry chance is 6.2%, and your listed Block chance (you have your shield equipped) is 5.1%. For the mob attacking you, its attack table will look like this.

Result

Chance

"Die Roll"

Miss

5.00%

0.01 - 5.00

Dodge

4.50%

5.01 - 9.50

Parry

6.20%

9.51 - 15.70

Glancing Blow

0%

—

Block

84.30%

15.71 - 100.00

Critical hit

0%

—

Crushing Blow

0%

—

Ordinary hit

0%

—

Now say that you elect to activate this warrior's Shield Block skill. Shield Block increases the warrior's Block chance by an additional 100%. For the next attack against your warrior, the mob's attack table now looks like this.

Note that both the chance of an ordinary hit, and the chance of a Critical hit, has been removed from the possible attack results entirely.

Elliot the Rogue is level 80, and is attacking a boss mob along with the rest of his raid group. He has stocked up on all sorts of +Crit Rating gear, so his crit chance against the boss mob is a whopping 30%. However, he didn't bring any +Hit Rating or +Expertise Rating gear with him, nor does he have the Precision talent; so the base chance for his attacks against a boss to Miss is 8%, the base chance for the same attacks to be Parried is 14%, and the base chance for the same attacks to be Dodged and be Blocked are 6.5% each. Since he is dual-wielding, he incurs an additional +19% miss chance on every autoattack swing; his total miss chance against a boss mob is 27%. Furthermore, he has a fixed 24% chance of glancing blows against bosses. When he attacks the boss mob from the front with a white-damage auto-attack, Elliot's attack table looks like this.

Note that despite his nominal "crit chance" of 30%, his miss chance from dual-wielding and his glancing blow chance due to the boss's high level mean that only 22% of his attacks are going to be critical hits. This conundrum is sometimes referred to as the Crit Cap—his chance to crit is capped at 22%, so 2% of his +crit bonus is wasted.

Result

Chance

"Die Roll"

Miss

27.00%

0.01 - 27.00

Dodge

6.50%

27.01 - 33.50

Parry

0%

—

Glancing Blow

24.00%

33.51 - 57.50

Block

0%

—

Critical hit

30.00%

57.51 - 87.50

Crushing Blow

0%

—

Ordinary hit

12.50%

87.51 - 100.00

Realizing his mistake, Elliot maneuvers around behind the boss mob to continue his attacks. From behind, a mob cannot parry or block, so Elliot's attack table now looks like this.

Result

Chance

"Die Roll"

Miss

8.00%

0.01 - 8.00

Dodge

6.50%

8.01 - 14.50

Parry

0%

—

Glancing Blow

0%

—

Block

0%

—

Critical hit

30.00%

14.51 - 44.50

Crushing Blow

0%

—

Ordinary hit

55.50%

44.51 - 100.00

Now that he's behind the boss mob, Elliot decides to Backstab it. A Backstab is a special ability; like other special abilities, the damage dealt by Backstab is displayed in yellow numbers. Special abilities, or yellow-damage attacks, do not incur the +19% miss penalty for dual-wielding, nor can they be Glancing Blows. Since Backstab is a yellow-damage attack, it doesn't use the standard Attack Table (c.f. below); however, if it did, Elliot's attack table would look like this.

Oh no! Elliot the Rogue has backstabbed the boss mob too hard, and has drawn aggro. The boss whirls around and raises his enormous fist in the air, threatening to pound poor little leather-clad Elliot into paste. Elliot's Agility does give him a decent dodge chance, but he doesn't have the Lightning Reflexes talent, nor does he have any gear that gives him Dodge Rating or Parry Rating. On the whole, things look grim. The boss mob's attack table against Elliot looks like this.

Result

Chance

"Die Roll"

Miss

4.40%

0.01 - 4.40

Dodge

72.30%

4.41 - 76.70

Parry

5.00%

76.71 - 81.70

Glancing Blow

0%

—

Block

0%

—

Critical hit

5.60%

81.71-87.30

Crushing Blow

0%

—

Ordinary hit

12.70%

87.31 - 100.00

Thinking quickly, Elliot activates his Evasion skill. This gives a whopping +50% increase to his Dodge chance. The mob's attack table now looks like this.

Holybrick, the level 80 Protection-specced paladin, has heard rumors that it's possible to become "Block Capped", so that he won't take unmitigated ordinary hits when fighting Raid Boss monsters. To this end, he strenuously accumulates piece after piece of gear that bestows bonuses to his Dodge Rating, his Parry rating, and even a rare piece that increases his Block Rating.

After much effort, he hovers over the Defenses section of his character sheet, and vs. level 83 and "skull" attackers sees the following: Dodge chance 9.6%, Parry chance 13.9%, Block chance 22.2%. He has also wisely invested 3 talent points in the Sanctuary talent, which reduces his chance to be crit by 6% -- since raid bosses have a nominal 5.6% crit chance vs. level 80 players, this effectively eliminates any danger of being crit during a boss fight.

Eager to try out his toughness, Holybrick boldly marches into a Raid instance with his comrades and pulls a Boss monster. The Boss's attack table against Holybrick looks as show to the left.

Clearly, Holybrick's gearing strategy has left him woefully vulnerable to unblocked hits.

Result

Chance

"Die Roll"

Miss

10.00%

0.01 - 10.00

Dodge

9.60%

10.01 - 19.60

Parry

13.90%

19.61 - 33.50

Glancing Blow

0%

—

Block

37.20%

33.51 - 70.70

Critical hit

0%

—

Crushing Blow

0%

—

Ordinary hit

29.30%

70.71 - 100.00

What is missing from this equation is his use of Holy Shield. The Holy Shield talent allows him to increase his block chance by 15% whenever he expends Holy Power. He quickly attacks the boss with Hammer of the Righteous to give himself 1 holy power, then spends it with Shield of the Righteous, thus triggering his Holy Shield. With Holybrick's Holy Shield up, the Boss's attack table now looks like this: (to the left)

Holybrick won't take unblocked hits as often, but sadly, he's still going to take them quite a lot of the time, even when he triggers Holy Shield. He is not "Block Capped" yet. Grimly determined, he saunters out to acquire even better gear.

Result

Chance

"Die Roll"

Miss

10.00%

0.01 - 10.00

Dodge

9.60%

10.01 - 19.60

Parry

15.90%

19.61 - 35.50

Glancing Blow

0%

—

Block

64.50%

35.51 - 100.00

Critical hit

0%

—

Crushing Blow

0%

—

Ordinary hit

0%

—

Later, after more wearisome effort, he has found a good deal of tank gear, and has reforged much of it so that it provides Mastery Rating. For a protection paladin, Mastery Rating increases his chance to block, and does so at a rate much higher than an equal amount of Dodge Rating or Parry Rating would increase his chance to dodge or parry. On his character sheet, his Block chance against level 83 or "skull" attackers is shown as a whopping 50.5%.

Now, Holybrick is ready. He steps back into the same Raid instance, pulls the same boss monster, and triggers his Holy Shield. Now, the Boss's attack table against him looks like this: (left)

Now, not only is he "Block Capped", but some of his block chance has actually gotten pushed off the end of the table. His nominal Block chance against this monster, with Holy Shield, should be 65.5%, but there is only "room" on the table for 64.5% of it. If he were to reduce his Mastery Rating a little bit so as to lose 1% of his Block chance, the Boss's attack table wouldn't change at all.

Melee special attacks, also called "Yellow-damage" melee attacks due to the color of their on-screen damage numbers, are not resolved the same way as white-damage melee attacks. Yellow damage attacks include all instant attacks (such as Overpower and Backstab) and all on-next-swing special attacks (such as Heroic Strike and Cleave).

The exact mechanism by which special attacks are resolved is not yet known. What is known, however, is that a special attack made against a mob or a shield-carrying player can be blocked and be a crit at the same time. This result is impossible under the mutually-exclusive attack results table described in the preceding section.

He corrected for all possible factors he could think of, and in the end discovered that the rate he got was consistent with his attack being resolved using two die rolls: A first roll to determine whether the attack missed (using the assumed miss chance for the mob targets he was attacking), and a second roll to determine whether an attack that didn't miss was a critical hit (using his tooltip Crit chance adjusted for the mob target's level).

If his data are accurate, and if the game mechanics for yellow-damage attacks haven't changed since the time that discussion thread was written, then there are at least two random numbers generated to determine the outcome of special attacks. It is unfortunate, though, that these tests were done with Backstab and not with a special attack that can be made against a mob from the front, e.g. Sinister Strike or Heroic Strike. Such data would be more useful, because attacks from the front can be parried and blocked.

A ranged attack cannot result in a dodge, parry, or glancing blow. (On their test realms at one point, Blizzard experimented with allowing a small dodge chance against ranged attacks, but this was considered too harmful to Hunters and the experiment was abandoned.) This means that ranged attacks can only miss, crit, be blocked, hit normally, or result in a crushing blow (crushing blows are limited to mobs).

A post made by Lactose on ElitistJerks shows strong evidence that Hunters do not use a single roll system for their ranged attacks.[2] Banshee's Curse, a debuff given by Banshee (Hyjal) reduced his chance to hit by 66%, giving him a Miss chance of 67.96% against a level 70 target. Since his tooltip Crit chance was 35.83%, in a one-roll system the only successful auto-shoot attacks should be crits; however, both Auto Shots and Multi-Shot successfully hit repeatedly without critting. This means that Hunters use at least a two-roll system for all of their ranged attacks.

The attacks of some monsters that do magic damage are actually treated as melee attacks, and use the standard melee auto-attack rules. For example, the melee attacks done by a fire elemental inflict fire damage, but they're resolved as an ordinary white-damage auto-attack—they can miss, be dodged, be parried, be blocked (as of Patch 3.0), and do double damage on a crit. The only difference between how a magic-damage melee auto-attack, and an ordinary physical damage melee auto-attack, is resolved is that if the target has any resistance to that school of magic, the same check is made to see if the damage is partially resisted as would happen from a spell.

Some monsters also have melee "specials" (the equivalent of yellow-damage attacks done by players) that do magic damage. For example, the Crystal Strike ability of the Erratic Sentries on the Isle of Quel'Danas inflicts Arcane damage, but is resolved as an ordinary melee special attack—it can miss, be dodged, be parried, and be blocked, and does double damage on a crit. The only difference between how a magic-damage melee special attack, and an ordinary physical damage melee special attack, is resolved is that if the target has any resistance to that school of magic, the same check is made to see if the damage is partially resisted as would happen from a spell.

A few player abilities, such as a paladin's Seal of Command, are likewise resolved as yellow-damage melee attacks that deal non-physical damage. The odds of the various attack results occurring with one of these attacks are determined the same as for physical melee attacks—the base chances are determined by the player's Weapon Skill with the wielded weapon, the miss chance is reduced by the player's Hit Rating, the chance to be dodged and parried is reduced by the player's Expertise, and the chance to crit is increased by the player's Agility and Crit Rating.

The Arcane Shot of a Hunter, and the Hammer of Wrath and Avenger's Shield talent of a Protection-specced Paladin, are resolved as ranged attacks that do non-physical damage. They can miss—rather than be "fully resisted"—and they do double damage on a crit. The only difference is that if a mob target is higher level than the player attacker, or if the target has any resistance to the school of magic used by the attack, the same check is made to see if the damage is partially resisted as would happen from a spell.

The odds of the various attack results occurring with one of these attacks are determined the same as for physical ranged attacks—the base chances are determined by the player's Weapon Skill with the wielded ranged weapon (in the case of Hunter abilities), the miss chance is reduced by the player's Hit Rating, and the chance to crit is increased by the player's Agility and Crit Rating.